Electromagnetic turnoff system for permanent magnets

ABSTRACT

A magnetic circuit made of a permanent magnet of high coercivity material, for example, barium ferrite ceramic material having a coercive force sufficiently high that the domains of the permanent magnet will not be reversed, and an electrical coil wound closely around the permanent magnet over its entire length. The electrical coil may be excited by a direct current of value and direction such that the magnetic field from the permanent magnet will be partially or completely neutralized, however, the domains of the permanent magnet will not be reversed and when the current in the coil is reversed from the first condition, the strength of the magnet becomes equal to the combined magnetic field from the permanent magnet and the magnetic field from the coil. This magnetic circuit is particularly useful for use in lifting magnets, although it is also applicable to magnets used for separating, holding, or otherwise exerting an external magnetic influence.

Benson June 19,- 1973 ELECTROMAGNETIC TURNOFF SYSTEM FOR PERMANENTMAGNETS [75 I Inventor: William H. Benson, Erie. Pa.

[73] Assignee: Eriez Manufacturing Company,

Erie, Pa.

[22] Filed: Apr. 7, 1972 [21] .Appl. No.: 241,974

Related US. Application Data [63] Continuation-impart of Ser. No.64,685, Aug. 18,

1970, abandoned.

[52] US. Cl.... 335/284, 335/289 [5]] Int. Cl. ..H01f 13/00 [58] Fieldof Search 335/284, 289, 290,

[56'] References Cited UNITED STATES PATENTS 3,089,064 5/1963 DeBennetot.....' 335/289 UX 3,146,381 8/I964 Moreau 335/289 UX 3,316,5144/1967 Radus et al. 335/291 3,428,867 2/1969 Becker 335/284 X PrimaryExaminer-George Harris Att0rneyCharles L. Lovercheck [57] ABSTRACT Amagnetic circuit made of a permanent magnet of high coercivity material,for example, barium ferrite ceramic material having a coercive forcesufficiently high that the domains of the permanent magnet will not bereversed, and an electrical coil wound closely around the permanentmagnet over its entire length. The electrical coil may be excited by adirect current of value and direction such that the magnetic field fromthe permanent magnet will be partially or completely neutralized,however, the domains of the permanent magnet will not be reversed andwhen the current in the coil is reversed from the first condition, thestrength'of the magnet becomes equal to the combined'magnetic field fromthe permanent magnet and the magnetic field from the coil. This magneticcircuit is particularly useful for use in lifting magnets, although itis also applicable to magnets used for separating, holding, or otherwiseexerting an external magnetic influence.

4 Claims, 4 Drawing Figures ELECTROMAGNETIC TURNOFF SYSTEM FOR PERMANENTMAGNETS CROSS REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part of application, Ser. No. 64,685, filed Aug. 18,1970 now abandoned.

I STATEMENT OF PRIOR ART Lifting or hoisting apparatus utilizingelectromagnets have been in operation for many years. The electromagnettype of lifting apparatus has at least two serious disadvantages:

. 1. It is required that a large amount of electrical energy be suppliedto the electromagnet in order to provide the lifting force and this isexpensive; furthermore, most of this energy must come out as heat, whichimpairs the efficiency of the magnet, shortens its life, and is diffcult to dispose of.

2. If the magnet is inadvertently de-energized, the load will fall,unless an expensive power back-up system is used.

Various prior lifting magnets have been proposed; for

example 'U.S. Pat. No. 3,316,514, 3,389,357; 3,089,064, 3,389,358, and3,441,807.

REFERENCE TO PRIOR ART US. Pat. No. 3,428,867 shows a magnetic circuitphysically similar to applicants circuit but it discloses a magneticmaterial which is of insufficient coercive force to retain the magneticdomains in their original position when a current in the coil isreversed. The said patent suggests that material usedshould have acoercive force of 900 ampere turns per inch (450 oersteds), whereas inmy invention, the permanent magnet material must have a coercive forceof at least 4,400 ampere turns per inch (2,200 oersteds) to preventde-magnetization.

OBJECTS OF THE INVENTION It is an object of the invention to provide animproved magnetic circuit.

Another object of the invention is to provide an improved magneticlifting device or other magnetic device for exerting an externalmagnetic influence.

A further object of the invention is to provide a magnetic circuit thatis simple in construction, economical to manufacture, and simple andefficient to operate.

GENERAL DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION OF THE DRAWINGSNow with more particular reference to the drawings, in FIG. 1 thepermanent magnet is shown supported by the pole pieces 12 and 13. Thesepole pieces may be of soft iron or steel. The permanent magnet 10 ismade of high coercivity material, such as barium ferrite, which is madeup of wafers stacked one on the other. A specific example of suitablemagnetic material is Indox V having a coercive force of 4,400 ampereturns per inch (2,200 oersteds). Indox V is a registered trademark ownedby the Indiana General Company. A coercive force in this range willprevent the magnetic domain of the permanent magnet from reversing anddemagnetizing the magnet so that when the current in the coil is such asto produce a reverse magnetomotive force to that of the permanentmagnet, the permanent magnet will retain its original magneticcondition. A coil 16 is disposed around the magnet as shown. The coilhas terminals 17 and 18 to which a D.C. voltage may be connected. Asuitable hoist can be connected to lifting eyes 40. A load 20 may belifted by the permanent magnet field alone or by the combined permanentmagnet and coil fields when coil current flows in a direction such as toaid the field of permanent magnet 10 indicated by arrows 30. When thecurrent is in a direction to aid the permanent magnetic field, amagnetic field due to the current flow will be induced in the stack ofpermanent magnets 10 by the coil in the direction indicated by arrows31. The resultant field is greater than the field produced by thepermanent magnet alone indicated by arrows 30 when the current is turnedoff; stated another way, when the field induced by the coil is inthesame direction asthe magnetic field of the per manent magnet, the sumof fields 30 and 31 will be stronger than that of the permanent magnetalone.

When the D. C. voltage on terminals 17 and 18 is reversed, as indicatedin FIG. 2, the permanent magnet field of magnet 10 will be partially orcompletely cancelled or neutralized by an opposite field 31 due to thecoil and the load 20 will drop, provided the net field has beensufficiently weakened to allow this.

In the embodiment of the invention shown in FIG. 3, a permanent magnetmade of a high coercivity material such as barium ferrite is shownsupported on the back plate Ill-with the polepieces 112 and 113,supported on the back plate to provide ends 114 and 115 to which a loadmay be attracted between these pole pieces and magnet pole piece 121.The coil 116 is wrapped closely around the magnet and extends entirelyfrom one end thereof to the other as does the coil 16 in the embodimentshown in'FlG. 1. Terminals 117 and 118 may have a source of electricalD.C. energy connected thereto whereby in one direction, the field 130from permanent magnet 110 is aided by the electromagnetic field 131 fromthe coil 116 to make a stronger combined magnet. In the other direction(FIG. 4), the magnetic field 130 from the permanent magnet field may becompletely or partially cancelled out by field 131 from the coil, sothat little or no force will be applied to the load and, therefore, theload 120 will not be supported. A suitable hoist can be connected to thelifting eyes 140.

The foregoing specification sets forth the invention in its preferredpractical forms but the structure shown is capable of modificationwithin a range of equivalents without departing from the invention whichis to be understood is broadly novel as is commensurate with theappended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A magnetic circuit comprising a permanent magnet,

a coil,

said coil being adapted to have a direct current pass therethrough andto produce a magnetic field through said permanent magnet,

said permanent magnet being made of a magnetic material having asufficiently high coercive force that the magnetic domains of saidmaterial will not change substantially when said current from said coilis passed therethrough in a direction to produce a field of a directionopposing said permanent magnet field,

said coil being adapted to have the said current therethrough reversedwhereby its magnetic field aids the field of said permanent magnet andtherefore produces a stronger magnet.

2. The magnetic circuit recited in claim 1 wherein said permanentmagnetic material is a material having a coercive force equal to orgreater than 4,400 ampere turns per inch.

3. The magnetic circuit recited in claim 1 wherein said coil covers theoutside surface of said permanent magnet to the extreme ends of saidmagnet.

4. The magnetic circuit recited in claim 3 wherein said ends of saidmagnet are adapted to attract a magnetic material thereto whereby saidmagnet may be used as a lifting magnet and means on said magnet forattaching it to a lifting member.

1. A magnetic circuit comprising a permanent magnet, a coil, said coilbeing adapted to have a direct current pass therethrough and to produceA magnetic field through said permanent magnet, said permanent magnetbeing made of a magnetic material having a sufficiently high coerciveforce that the magnetic domains of said material will not changesubstantially when said current from said coil is passed therethrough ina direction to produce a field of a direction opposing said permanentmagnet field, said coil being adapted to have the said currenttherethrough reversed whereby its magnetic field aids the field of saidpermanent magnet and therefore produces a stronger magnet.
 2. Themagnetic circuit recited in claim 1 wherein said permanent magneticmaterial is a material having a coercive force equal to or greater than4,400 ampere turns per inch.
 3. The magnetic circuit recited in claim 1wherein said coil covers the outside surface of said permanent magnet tothe extreme ends of said magnet.
 4. The magnetic circuit recited inclaim 3 wherein said ends of said magnet are adapted to attract amagnetic material thereto whereby said magnet may be used as a liftingmagnet and means on said magnet for attaching it to a lifting member.